The present invention relates to the field of patient-controlled drug administration devices. More specifically, it relates to an apparatus for administering a medicinal agent to a patient that allows the patient to provide a precisely controlled self-administered bolus dose of the agent in addition to a continuous flow of the agent.
In many clinical situations, it is necessary to administer a continuous flow of a medicinal agent to a patient, and to augment the basal flow periodically or intermittently with a supplemental or "bolus" dose of the agent. This regimen is frequently used in the management of chronic pain, where a continuous flow of an analgesic is maintained by infusion, but a bolus dose of the analgesic is infused at selected times when the patient experiences a sharp increase in the pain. Because most analgesics must be carefully administered to avoid overdosing, the timing and the volume of the bolus doses must be carefully controlled. This control is often exercised by a medical practitioner who administers the bolus dose when it is deemed necessary or desirable.
In chronic care situations, or in home care situations, it is impractical, in many cases, to have a medical practitioner available whenever a patient wants or needs a supplemental bolus dose. Consequently, a number of drug administration devices have been developed that allow the patient to self-administer a controlled bolus dose. These devices (sometimes called patient-controlled administration devices, or "PCA" devices) typically provide a bolus dose that is no more than a predetermined volume, and they also typically include a "lock-out" mechanism, by which is meant a mechanism that limits the frequency of bolus dose administration, or that limits the total bolus dose volume administered over a selected time interval. Some, but not all, prior art PCA devices also allow a controlled continuous flow of the agent between bolus doses. Examples of prior art PCA devices are disclosed in the following U.S. Pat. No.: 4,398,908--Siposs; U.S. Pat. No. 4,544,371--Dormandy, Jr. et al.; U.S. Pat. No. 4,548,607--Harris; U.S. Pat. No. 4,601,707--Albisser et al.; U.S. Pat. No. 4,634,427--Hannula et al.; U.S. Pat. No. 4,668,231--de Vries et al.; U.S. Pat. No. 4,699,615--Fischell et al.; U.S. Pat. No. 4,828,551--Gerler et al.; U.S. Pat. No. 4,898,584--Borsanyi et al.; U.S. Pat. No. 4,898,585--Borsanyi et al.; U.S. Pat. No. 5,011,477--Winchell et al.; U.S. Pat. No. 5,061,243--Winchell et al. and U.S. Pat. No. 5,304,153--Tsujikawa.
Many of the prior art PCA devices are specifically designed to be implantable within the patient's body. For example, of the above-listed patents, the following disclose implantable devices: Dormandy, Jr. et al. '371, Harris '607, Hannula et al. '427, de Vries et al. '231, Fischell et al. '615, Borsanyi et al. '584, and Borsanyi et al. '585. This approach, which requires a surgical procedure for the implantation, may not be suitable for all patients, especially those whose need for the drug is temporary, even if relatively long-term.
Many of the non-implantable PCA devices that have been developed to date are bulky or complex. Such devices are typically expensive to manufacture, and therefore not suitable for single-patient disposable applications. Other devices, while providing convenient delivery of bolus doses on patient demand, require a parallel system for delivery of a continuous flow. An example of the latter type of device is disclosed in U.S. Pat. No. 5,304,153--Tsujikawa.
Thus, there has been a need for a non-implantable PCA device that provides convenient, measured, patient-controlled bolus doses of a therapeutic agent, and that also allows for a regulated continuous or basal flow of the agent. Furthermore, it would be advantageous if such a device were to have a "lock-out" mechanism that limits the total bolus dose volume delivered at any one time or over any specified time interval. In addition, it would be advantageous for such a device to be simply constructed and easily and inexpensively manufactured, so that it may be made as a single-patient disposable apparatus.